Conus (Lautoconus) ventricosus rhodesensis, Psarras & Merle & Moissette & Koskeridou, 2024

Psarras, Christos, Merle, Didier, Moissette, Pierre & Koskeridou, Efterpi, 2024, The Pleistocene Conidae (Mollusca: Gastropoda) from the island of Rhodes (Greece) and their palaeoecological significance, Geodiversitas 46 (11), pp. 423-444 : 429-432

Conus (Lautoconus) ventricosus rhodesensis n. subsp.

( Figs 3-5 )

urn:lsid:zoobank.org:act:C6666488-2863-45A9-A483-24D5A2598D3D

Chelyconus pelagicus – Chirli & Linse 2011: 165, pl. 56, figs 1a-d, 6 (non Brocchi, 1814).

Chelyconus striatulus – Chirli & Linse 2011: 165, pl. 56, figs 2a-d (non Brocchi, 1814).

Lautoconus mediterraneus – Chirli & Linse 2011: 166, pl. 56, figs 3a-d. (non Hwass, 1792).

ETYMOLOGY. — From the island of Rhodes, where the species has been found.

TYPE LOCALITY. — Tsampika, Tsampika section, Rhodes, Greece.

TYPE HORIZON. — Ladiko-Tsampika Fm, Pleistocene, Rhodes, Greece.

TYPE MATERIAL. — Greece • 9 specimens; Rhodes ; Ladiko-Tsampika Fm, Tsampika section, TSS block; Lower Pleistocene (Gelasian) to Upper Pleistocene; holotype: MNHN.F.A88160 ; paratypes: MNHN.F.A88161-A88168 • 1 specimen; Ladiko-Tsampika Fm, Tsampika section, TSS 2; Lower Pleistocene (Gelasian) to Upper Pleistocene; paratype: AMPG (IV) 4048 • 5 specimens; Ladiko-Tsampika Fm, Tsampika section, TSS south; Lower Pleistocene (Gelasian) to Upper Pleistocene; paratypes: AMPG (IV) 4049-4053 .

OTHER MATERIAL EXAMINED. — Greece • 14 specimens; Rhodes ; Ladiko-Tsampika Fm , Tsampika section, TSS 2; AMPG (IV) 4034- 4047 • 2 specimens; Rhodes ; Ladiko-Tsampika Fm , Tsampika section, TSS 3; Lower Pleistocene (Gelasian) to Upper Pleistocene; AMPG (IV) 4054, 4055 • 2 specimens; Rhodes ; Ladiko-Tsampika Fm , Tsampika section, TSS 1; Lower Pleistocene (Gelasian) to Upper Pleistocene; AMPG (IV) 4056, 4057 • 1 specimen; Rhodes ; Kritika Fm , Kritika Hospital ; Lower Pleistocene (Gelasian) to Upper Pleistocene; MNHN.F.A90344 • 104 specimens; Rhodes ; Ladiko-Tsampika Fm , Tsampika section; Lower Pleistocene (Gelasian) to Upper Pleistocene MNHN.F.A90343 (lot) • 1 specimen; Rhodes ; Archangelos Fm , Malona; Lower Pleistocene (Gelasian) to Upper Pleistocene; AMPG (IV) 4060 .

STRATIGRAPHIC RANGE. — Gelasian (Lower Pleistocene) to Upper Pleistocene of Rhodes, Greece ( Chirli & Linse 2011; this work).

DESCRIPTION

Shell

Small to moderately-sized shells (maximum length of about 25.7 mm), with conical spire of variable height. Spire whorl outline slightly concave to slightly convex. Early spire whorls conical with spiral grooves on sutural ramps. Later spire whorls conical, straight to slightly convex, with occasional spiral grooves on sutural ramp, sometimes slightly striated to elevated. Shoulder angulated to smooth, with maximum diameter on shoulder to just below shoulder. Subsutural flexure shallow, moderately curved, nearly symmetrical. Spiral grooves and cords along the last whorl, intense at anterior third of last whorl.

Colour pattern

Colour pattern of the spire whorls consists of one level of pigmentation of broad axial to thin flammulae. The pattern on the shoulder consists of a non-fluorescent band at carina. The axial flammulae levels of pigmentation of the spire whorls rarely overlap the non-fluorescent band (E3). The colour pattern on the last whorl consists of spiral rows of dashes, of variable length ( Fig. 4 ), alternating with non-fluorescent dots. Fluorescent bands exist in different heights and widths. Usually there is one band in the middle whorl and one in the anterior part of the last whorl, separated by a non-fluorescent band. In this fluorescent band, the spiral rows of dashes are less long and dense.

REMARKS

We have examined 140 specimens. This group shows a great morphological diversity, as there are both shells with elevated spires and low spired ones and the spiral whorls can be striated or smooth ( Fig. 3 ). Nevertheless, the residual colour patterns are similar in all specimens studied. There are some specimens ( Fig. 4 ) with aberrant colour patterns, but we provisionally consider them as intraspecific variations.

Recently, Abalde et al. (2023) found evidence of at least three mitochondrial ‘ Conus ventricosus ’ clades corresponding to three cryptic species. They ( Abalde et al. 2023) provisionally named those clades based on the colours used on their analyses (with the main clades being green, violet, cyan), with the ‘green’ and ‘cyan’ clades being present today in Greece, while the ‘violet’ clade is present in central and western Mediterranean ( Abalde et al. 2023) (see colours in Fig. 5 ). The likelihood of many cryptic species in the Mediterranean specimens ( Tenorio et al. 2020; Abalde et al. 2023) is evidenced by mitochondrial studies, but the morphology and colour pattern characteristics of those clades remain unclarified, since specimens of the same lineage present greatly diversified morphology and pattern variations ( Fig. 5C 4-C 5 ) ( Abalde et al. 2023).

The Pleistocene juvenile forms ( Fig. 5A ) are rather similar to the extant C. (Lautoconus) ventricosus Gmelin, 1791 sensu lato. However, comparing the Pleistocene adult specimens with extant adult of “ C. ventricosus ”, there are some differences in the colour patterns. The spiral rows of extant adult “ Conus (Lautoconus) ventricosus ” are more numerous and the flakes, as well as the blotches, are axially coordinated, sometimes in a zigzag pattern. Given the supposed great morphological and colour pattern variability of “ Conus (Lautoconus) ventricosus ”, the studied specimens could be attributed to this species, but the molecular phylogeny results of Abalde et al. (2023) are troubling from a palaeontological perspective, because the unnamed cryptic species cannot be distinguished using shells characters ( Abalde et al. 2023). On the other hand, we prefer to avoid erecting a new species, as the Pleistocene specimens are geologically young (2 Ma (Kritika) to 140 ka (Tsampika); Moissette et al. 2016; Cornée et al. 2018) and could belong to one of the extant cryptic species mentioned in Abalde et al. (2023). Therefore, taking account of the differences of colour patterns observed in the Pleistocene specimens, we erect a new chronostratigraphic subspecies Conus (Lautoconus) ventricosus rhodesensis n. subsp. as an ancestral subspecies of one of the ‘ C. (Lautoconus) ventricosus ’ clades. The concept of chronosubspecies is related to the phyletic gradualism model of evolution, and it also relies on an extensive fossil record since morphological changes accumulate over time. It is widely used by the palaeontologists (e.g., Ward & Kennedy 1993 for the ammonites; Fordinál 1997 for the bivalves; Merle et al. 2011 for the gastropods Muricidae ); Saupe & Becker 2022 for the conodonts).

The pattern of Conus (Lautoconus) ventricosus rhodesensis n. subsp. could also be compared with other species considered as Conilithes Swainson, 1840 , such as Conilithes sp. and Conilithes striatulus ( Brocchi, 1814) from the Tortonian of Crete ( Psarras et al. 2021), both of which display patterns of dashes along the last whorl. The outline of the juvenile Conus (Lautoconus) ventricosus rhodesensis n. subsp. also resembles that of several extinct Conilithes Swainson, 1840 , the main difference being that the sutural ramps are smooth in Conilithes , whereas Conus (Lautoconus) ventricosus rhodesensis n. subsp. has spiral grooves on the sutural band. Conilithes striatulus ( Brocchi, 1814) from the Pliocene of Italy has a similar pattern ( Pavia et al. 2022: fig. 26g), but has an angulated shoulder and a coeloconoid suture, all features that diverge from the subgenus Conus (Lautoconus) . The two species identified by Chirli & Linse (2011) as Chelyconus striatulus ( Brocchi, 1814) and Chelyconus pelagicus ( Brocchi, 1814) are both morphologically similar to Conus (Lautoconus) ventricosus rhodesensis n. subsp. and have similar patterns of spiral rows of dashes.

Conus (Lautoconus) ventricosus rhodesensis n. subsp. has been observed in several areas on Rhodes, namely Kritika (Gelasian), Faliraki, Malona, Lardos, and Ladiko ( Chirli & Linse 2011; personal observations). It seems that this subspecies was present on Rhodes throughout the early and late Pleistocene.

Figures

FIG. 3. — Conus (Lautoconus) ventricosus rhodesensisn.subsp.from the Pleistocene of Tsampika,Rhodes (Greece) under natural (A1, A2, A4, A5, B1, B2, B4, C1, C2, C4, D1, D2, D4, D6, E1, E2, E4, F1, F2, F4, G1-G4, H1, H2, I1, I2, I4, J) and UV (A3, B3, B5, C3, D3, D5, E3, F3, F4, I3) light: A, holotype MNHN.F.A88160; B-J, paratypes;B, MNHN.F.A88161; C, MNHN.F.A88162; D, MNHN.F.A88163; E, MNHN.F.A88164; F, MNHN.F.A88165; G, MNHN.F.A88166; H, MNHN.F.A88167; I, MNHN.F.A88168; J, AMPG (IV) 4048, protoconch of juvenile shell. Scale bars: A-I, 1 cm; J; 500 μm.

FIG. 4. — Specimens of Conus (Lautoconus) ventricosus rhodesensis n. subsp.from the Pleistocene of Rhodes (Greece),displaying aberrant patterns under natural (A1, A2, A5, A6, B1, B3, B4, B6) and UV (A3, A4, B2, B5) light: A, paratype AMPG (IV) 4053, Tsampika: a pattern of almost continuous spiral lines; B, specimen AMPG (IV) 4060, Malona: a pattern of very dense and small spiral dashes. Scale bars: A1-A5, B1-B5, 1 cm; A6, 500 μm; B6, close up view of B1, not to scale.

FIG. 5. — Colour pattern comparison between the extant Conus (Lautoconus) ventricosus complex species (natural light) clades (A, C1-C4) and Conus (Lautoconus) ventricosus rhodesensis n. subsp. from the Pleistocene of Tsampika, Rhodes (Greece) (UV light, inverted colours) (B). Thin dashed lines (A1, B1) include non-fluorescent bands, thick dashed line indicates the included spiral row of dashes. Encircled areas (A2, B2) are non-fluorescent spiral snowflakes in between the spirally arranged dashes. Depiction of five specimens of “Conus ventricosus” mitochondrial clades (green, violet and cyan, the latter divided into red and blue) of Abalde et al. 2023 (C). Note that specimens of the same clade have very different morphological and colour pattern characteristics (C3-C5). A, AMPG (IV) 4033,Artemis,east Attica,Recent,Greece;B, holotype MNHN.F.A88160, Tsampika,Rhodes;C1, BAU_1550.1,Koutsomiti island, Astypalaia,Greece;C2, SC002, Punta Regilione-Marina di Modica,Sicily, Italy; C3, CR18, Kakkos Bay, south-east Crete, Greece; C4, CR23, Kakkos Bay, south-east Crete, Greece; C5, CR009, Plaka, north-west Crete, Greece. Specimen figures C1-C5 from Manuel J. Tenorio and Samuel Abalde. Scale bars: 1 cm.